Embodiments of the present invention relate to a voltage controlled oscillator (VCO). In particular, embodiments of the present invention relate to a millimeter-wave wideband VCO system implemented in CMOS (complimentary metal oxide semiconductor).
There is a tremendous potential in terms of multi-gigabit wireless transmission using the unlicensed frequency-band—i.e., approximately 57-64 GHz (Giga-Hertz) in the United States and approximately 59-64 GHz worldwide—for high-speed data transfer between storage devices, point-to-point video, HDTV, wireless personal area networking (WPAN) applications, and the like.
For a low-cost CMOS implementation, it is difficult to achieve approximately 7-8 GHz tuning range using a single VCO along with a single varactor. The varactors commercially-available in CMOS are usually MOS varactors and, hence, the capacitance range is approximately less than 100% of the desired average value. Further, noise performances of large-sized varactors tend to perform poorly. Both the increased size of varactor and the reduced length of tuning inductor demand a better design to achieve the desired multi-channel wide band operation.
Many known design options fail to provide the needed multi-channel wide band solution. For example, a switched-varactor system (as shown in FIG. 1), a switched-inductor system, and an active-inductor-based VCO system enable multi-band operations. Unfortunately, these designs are limited to an operating frequency of a maximum of 10-20 GHz.
For instance, switched-inductor topology is not possible, because of increased switch loss, high switching capacitance for proper band switching, and low-Q resonance. Switched-varactor solutions (again, for example, as illustrated in FIG. 1) are difficult to implement in CMOS technologies; for instance, at greater than approximately 50 GHz, off-state capacitances inject noises and reduce the required tuning length. In fact, the switched-varactor solution is quite similar to a single VCO with a large varactor and, as a result, has the same disadvantages; specifically, the output power, reliability, and phase noise are sacrificed to obtain a simpler and more compact solution.